Variable displacement pump



May 18, 1965 R. E. RAYMOND VARIABLE DISPLACEMENT PUMP Filed May l0, 19624 Sheets--SheeI l ATTORNEYS May'lS, 1965 R. E. RAYMOND VARIABLEDISPLACEMENT PUMP 4 Sheets-Sheet. 2

Filed May l0, 1962 m fwu.,

ATTORNEYS INVENTOR ROBERT E. RAYMOND Q NO May 18, 1965 R. E. RAYMONDVARIABLE DISPLACEMENT PUMP 4 Sheets-Sheet 5 Filed May l0, 1962 INVENTORROBERT E. RAYMOND ATTORNEYS May 18 1955 R. E` RAYMOND 3,183,849

VARIABLE DISPLACEMENT PUMP Filed May' l0, 1962 4 Sheets-Sheet 4 ROBERTE. RAYMOND ATTORNEYS United States Patent O 3,133,849 VARIABLEDEPLACEMENT PUMP Robert E. Raymond, Zanesville, Ohio, assigner toHydro-Kinetics, Inc., Zanesville, hio Filed May 10, 1962, Ser. No.187,325 8 Claims. (Cl. 10S-173) This invention relates generally tohydraulic machines and particularly to a novel piston type variabledisplacement pump.

In general, the pump of the present invention comprises a housing andcylinder barrel that support a plurality of axially disposed cylindersincluding side walls provided with intake ports and a plurality ofpumping pistons mounted for axial reciprocating movement in thecylinders. The housing further supports an axially shiftable cam indriving engagement with said pistons and means for moving the cam andpistons to various axial positions whereby the effective stroke of thepistons, relative to the lixed position intake ports is increased ordecreased to vary the displacement and volumetric delivery of the pump.

As another aspect of the present invention the pump includes twooppositely acting annular piston and cylinder means mounted in thehousing means which comprise hydraulic means for axially moving andpositioning the previously mentioned cam and pumping pistons relative tothe intake ports.

As another aspet of the present invention the pump includes twooppositely acting springs mounted in the housing means which serve toconstantly bias the pumping pistons towards the cam and which constantlybias the cam and pumping pistons towards the position .of minimum pistonstroke.

As another aspect of the present invention, the pump including novelapparatus for transferring oil from a removable cylinder barrel to thepump housing which apparatus includes novel pressure biased hollowoutlet members movably mounted in the pump housing and in sliding sealedengagement with the cylinder barrel.

As another aspect of the present invention, the pump includes novelmounting means for supporting a removable cylinder barrel in the pumphousing, said mounting means being in the form of longitudinallyextending rail bearings that not only absorb piston side thrust but, inaddition, absorb torque and serve as keys against barrel rotation.

As another aspect of the present invention, the pump includes novelmeans for transferring piston thrust reaction forces to the pump housingin the form of a plurality of reaction plugs which serve to isolate thecylinder barrel pulsating piston forces.

As another aspect of the present invention, the pump includes aplurality of reaction plugs which are selfaligning since they freelyengage the pump housing at any location dictated by the aligned positionof the cylinder barrel on its longitudinally extending rail bearings.This eliminates costly alignment problems.

As another aspect of the present invention, the pump includes aplurality of reaction plugs that not only serve to transfer individualpiston reactionforces to the pump housing but also serve the additionalfunction of housing outlet check valve assemblies.

As another aspect of the present invention, the pump includes a novelvariable displacement control spring arrangement whereby a singlecontrol spring is utilized to bias the pumping pistons against thedriving cam. The same control spring also serves to bias the previouslymentioned reaction plugs against the pump housing.

As another aspect of the present invention, the pump comprises a novelpiston return apparatus that forces the "ice piston to follow a drivingcam. This apparatus includes a yoke that engages each piston, a yokereaction plug mounted in the cylinder barrel, and a yoke reaction springfor biasing the plug and yoke against the pistons. This eliminates theneed for individual piston return springs and permits a more compactapparatus.

As another aspect of the present invention, the pump comprises a novelcomposite piston shoe construction formed of nylon or the likesurrounded by a steel casing, the latter being crimped around a ballshaped base on the piston. This shoe construction serves the dualfunction of preventing the nylon shoe portion from splitting andretaining the shoe on the piston. This results in a piston shoe withsufficient compression strength and a low coefficient of friction.Moreover, the shoe is self-aligning and accommodates foreign materialswithout abrading the driving cam.

As another aspect of the present invention, the pump includes a novelcontrol apparatus that automatically meters a control flow of oil to thepreviously mentioned annular piston that shifts the driving cam. Thecontrol apparatus is adapted to automatically vary the effective strokeof the pistons responsive to variations in the outlet pressure to theload whereby oil is delivered to the load at substantially constantpressure.

As another aspect of the present invention, the control l apparatusmentioned in the previous paragraph can readily be removed and othercontrol apparatus substituted' therefor to establish other desiredconditions at the load other than the substantially constant pressureconditions provided by the control apparatus discussed in the previousparagraph.

As another aspect of the present invention, the pump is modified toinclude a novel shock relief apparatus for the variable displacementcontrol mechanism which apparatus is responsive to the excessive ratesof change of pressure and to excessive flow rates. This shock controlapparatus comprises a modified pressure biased holloW outlet member thatincludes a shock detection plate provided with an orice of sufficientsize to accommodate higher rates of flows encountered during shockconditions.

As another aspect of the present invention, one modication of the pumpincludes an annular cam driving cylinder that extends circumferentiallyaround the casing of the pump and includes an intake opening for arelatively hot flow of control oil and an outlet passage, on theopposite side of the casing means, for releasing the control How to theexterior of the casing means. This annular cylinder and passagearrangement not only serves to cool the relatively hot control flow ofoil by passing it circumferentially around the outer regions of thecasing, in heat exchange relationship with the environment, but alsoprovides built in means for delivering the control ow from a controlmechanism mounted on the top of the casing means to a subplate mount onthe bottom of the casing means from where the control flow can beconveniently returned to an external reservoir.

As still another aspect of the present invention, the pump includes aremovable cylinder barrel provided with an integrally moulded annularmanifold that functions in a novel manner to collect the outlet oil fromthe cylinders and transfer it to the pump housing.

Further objects and advantages of the present invention will -beapparent from the following description, reference being had to theaccompanying drawings wherein a preferred form of embodiment of theinvention is clearly shown.

In the drawings:

FIG. l is a side sectional view of a variable displacement pumpconstructed in accordance with the present 3l invention, the sectionbeing taken along the plane 1 1 of FIG. 2;

FIG. 2 is an end sectional view of the pump of FIG. 1, the section beingtaken along the line 2 2 of FIG. 1;

FIG. 3 is a second end sectional view of the pump of FIG. 1, the sectionbeing taken along the line 3 3 of FIG. 1;

FIG. 4 is a third end sectional view of the pump of FIG. 1, the sectionbeing taken along line 4 4 of FIG. l;

FIG. 5 is a fourth end sectional view of the pump of FIG. 1, the sectionbeing taken along the line 5 5 of FIG. 1;

FIG. 6 is a top elevational view, partially in section, of the pump ofFIG. 1, the section being taken along the line 6 6 of FIG. 1; and

FIG. 7 is a partial top sectional View showing one of the studs thatmounts the cylinder barrel in the casing means of the pump, the sectionbeing taken along the line 7 7 of FIG. 4.

Referring in detail to the drawings, a variable displacement pumpconstructed in accordance with the present invention is illustrated inFIGS. 1 and 6 and comprises a housing means indicated generally at 22and a rear housing portion indicated generally at 24. The two casingportions are joined together at the central portion of the pump'by aplurality of studs 26 seen in FIG. 6.

A drive shaft 28 is mounted in the forward end of the housing means by atapered roller bearing assemblies 30 and 32 which assemblies are pressedinto recesses 34 and 36.

An oil seal 38 is pressed into a recess 40 in the housing and includesan annular resilient element 42 that wipes the periphery of drive shaft28.

As seen in FIG. 1 the inner end of drive shaft 28 slidably carries camindicated generally at 44 which includes a female spline 46 thatslideably receives a male spline 48 on shaft 28 for preventing rotationof cam 44 relative to shaft 28. The shaft 28 is retained against axialmovement by a nut 52 and a shoulder 53 that engage the inner races ofbearing assemblies 30 and 32.

With continued reference to FIG. 1, cam 44 includes an inclined surface54 which engages a plurality of nylon shoes 56, the latter includingsockets 58 which form pivotal ball joints with ball-shaped ends 60formed on a plurality of pumping pistons 62.

Each of the nylon shoes 56 is surrounded by a metal casing 64 that iscrimped around an annular upper nylon bearing portion 65. Each metalcasing 64 also includes an inwardly extended annular protrusion 66 thatsnaps into an annular recess 68 formed in the base of the nylon shoeportion.

With reference to FIGS. 1 and 7, a cylinder barrel indicated generallyat 70 is removably mounted within the casing means by means of aplurality of barrel mounting studs 72 having threads screwed intothreaded holes 73 circumferentially spaced around the rear end ofcylinder barrel 70. Lock washers 76 are provided in the counter sinks 74between the heads of studs 72 and the rear wall of casing portion 24.

The barrel mounting studs 72 not only absorb piston side thrust reactionimposed on the cylinder barrel, but, in addition, function as keysagainst cylinder barrel rotation and thereby serve to absorb torque.

Pistons 62 are disposed in respective barrel cylinders 78 which receivelow pressure oil or hydraulic fluid via intake 80 in base 82, passage 84in front housing portion 22, the inner chamber 86 within the housing andthe intake ports for each cylinder, two of which are seen at 8S and 88Ain FIG. 1.

Intake port SS-A is shown with its respective piston 62 at the bottom ofa stroke at which position the piston has uncovered intake port 88-A anddrawn fluid into its cylinder. Intake port 88, however, is closed sinceits respective piston is at the top of its stroke.

As seen in FIGS. 1 and 3, each of the cylinders 78 includes a respectivereaction plug, indicated generally at 90, in free self-aligningengagement with the inner end surface 92 of rear housing portion 24.

Each reaction plug 98 is provided with a central bore 94 that carries anoutlet ball check valve 96 which is freely retained in bore 94 by athreaded plug 98.

Each threaded plug 98 includes a seat portion 100 and a longitudinalpassage 102, the latter communicating with a radial passage 103 and anannular passage 104 formed in the outer wall of reaction plug 90.

With continued reference to FIG. l, the bore 94 in each reaction plugincludes a valve stop 106 andy a compression spring 108 which serve tolimit the stroke of the ball and bias it towards a closed position.

Pressurized oil from cylinders 78 is discharged to the exterior of thepump, in a unique manner, through a pressure biased outlet member 110which includes a central passage 112 that communicates with highpressure discharge passage 114 that in turn leads to an outlet hole 116formed in base 82.

As seen in FIG. 1, outlet member 110 includes a foot portion providedwith a surface 118 that is in sealed er1- gagement with a longitudinallyextending surface 126 formed in the outer wall of cylinder barrel 70.

With continued reference to FIGS. 1 and 2, pressure biased outlet member110 includes a piston surface 124 that causes the pressurized hydrauliciluid in passage 112 to bias the surface 118 on outlet member 110downwardly into sealed engagement with longitudinally extending surface120 on barrel 7u.

A spring 126 augments the biasing force of the high pressure oil onpiston surface 124 and also serves to retain surface 118 inV sealedengagement with surface 120 at low pressures and at the outset ofoperation.

The outer peripheral surface of outlet member 110 is provided with anannular seal 128 and a threaded plug 129 is screwed into the holeforming passage 112 and includes an inner prOtrusion that forms aretainer for the end of spring 126.

With reference to FIGS. 1 and 4, pressurized oil from the pumpingcylinders 78 is released from longitudinal passages 102 in reactionplugs 90 via a plurality of small radially extending passages 103, FIG.4, annular recesses 104, an annular manifold 134, cylinder barrel outletport 122, radial passage 112 through outlet member 110, passage 114, andbase outlet hole 116 to the load.

Pressurized oil is also released to a variable displacement hydrauliccontrol unit indicated generally at by a second pressure biased outletmember 110-A, FIGS. l and 2, which is identical to outlet member 110previously described. It will be noted that outlet member 11u-A includesa base surface 136 that is hydraulically biased into sealed engagementwith a longitudinally extending surface 138 formed in the outer wall ofcylinder barrel 70. Outlet member 11G-A is biased downwardly againstlongitudinally extending surface 138 by a force exerted on pistonsurface 124 by pressurized oil in a passage 140.

Referring to FIG. 1 the displacement is varied by shifting caml 44 whichis hydraulically accomplished by a cam driving piston and cylinder meansindicated generally at 145. The rear housing portion 24 and an annularcam driving piston 147 form an annular cam driving cylinder 149 thatreceives a pressurized flow of control oil from a flow control apparatus13S later to be described in detail herein.

The cam 44 is biased towards the rear of the housing by a cam returnspring 151 and by an annular reaction piston and cylinder means 153. Thespring 151 is interposed between a spring mounting recess 155 and anaxially shiftable cam mount indicated generally at 161.

Cam mount 161 is keyed against rotation by a pin 258 mounted by pressfit in a hole in front housing portion 22 with the inner end of the pinextended into a longitudinal slot 256 in the periphery of cam mount 161.

With reference to FIGS. 1 and 3, cam mount 161 includes an annularreaction piston portion 163 that is slideably mounted in an annularreaction cylinder 165 formed by front housing portion 22 and annularreaction piston portion 163.

Pressurized oil is delivered to cam reaction cylinder 165 via annularmanifold 134, radial passage 112, outlet passage 114, and intersectingdrilled holes 167 and 169.

In view of the above it will be understood that cam mount 161 and cam 44are constantly biased toward the cam driving piston and cylinder 149 byboth the spring 151 and the reaction piston and cylinder means 153. Theannular area of the driving piston 147 is, however, suciently greaterthan the annular area of the reaction piston 163 whereby the controlflow of Oil at manifold pressure exerts suficient force to shift cammount 161 against the combined force of reaction piston and cylindermeans 153 and cam return spring 151.

It should be pointed out that reaction piston and cylinder means 153permit the use of a relatively light cam return spring 151 underoperating loads, the spring being required to return the pumping pistonsto the maximum effective stroke position under low pressure startingconditions.

As seen in FIG. 1, a tapered roller bearing 171 is carried by cam mount161 and includes a bore 173 that receives a shank portion 175 of bearing171.

Referring particularly to FIGS. 1 and 6, pressurized oil is deliveredthrough the control apparatus 135 to the cam driving piston and cylindermeans 146 via passage 140, passage 144, orifice 147, spool cylinder 148,radial passage 138 in spool housing 151, lateral passage 154 in controlblock 156, longitudinal passage 158 in control block 156, verticalpassage 160 in control block 156, and passage 162 in the pump housingwhich connects to cam driving cylinder 149.

Cam driving cylinder 149 is continuously drained back to tank viapassage 181, small control orifice 232, FIGS. l and 2, passage 183, andoutlet port 185 which is connected to a line back to tank.

Referring particularly to FIGS. 1, 4 and 6, a stationary spool housing151 is mounted in control block 156' and carries a longitudinallyshiftable spool member 164 that is normally biased towards a closedposition by a spring 166, the latter being contained in a spring housing168 that is threaded into control block 156 at a threaded hole 170.Compression spring 166 is selectively compressed or released bymanipulating a control knob 172 that includes a shank 174 in threadedengagement with spring housing 168 at a threaded hole 176. As seen inFIG. 1, a radial passage 178 extends through control block 156 and rearhousing portion 24 to provide a drain back to tank for any hydraulicfluid that may leak between the outer surface of control spool 164 andthe inner surface of spool cylinder 148.

Control block 156 is mounted on housing 20 by means of a plurality ofstuds 192 as seen in FIG. 6. It will be understood that other types ofcontrol apparatus and various types of load conditions, can be readilymounted on `the pump merely by unscrewing the studs and replacingcontrol block 156 with a modified version.

The pumping pistons 62 are returned and biased against cam 44 in a novelmanner, by means of a single centrally disposed piston return rod 194,FIG. l, which includes aspherical foot portion 196 that ts into socket198 formed in a nylon piston return yoke 202. Yoke 202 includes aplurality of circumferentially spaced sockets 204 that receive thepreviously described crimped casing p0rtions 64 of thepiston shoes 62 tothe rear sides of piston foot casings and in turn receives force frompiston return rod 194 via the pivot joint formed by foot portion 196 andsocket 198.

A compression spring 210 is disposed between a shoulder 214 on the rearend of piston return rod 194, a shoulder 212 on a spring retainer plug216 which in turn bears against the front side of spider 143. Spider 143is restrained from rearward movement by retaining rings 220 formed onthe ends of reaction plugs 90. It should be pointed out that reactionplugs are fitted loosely into respective holes 222 in spider 143 and arein free engagement with the inner surface 92 of the housing whereby theplugs are self-aligning with respect to pump cylinders 78.

The ends of passages 154 and 158 in control block 156 are closed bythreaded plugs 224 and 225 respectively.

The pump may include a shock relief feature that is provided by adding ashock detection plate 25,2 provided with a relatively small orifice 254to pressure biased outlet member liti-A. During normal operatingconditions orifice 254 is large enough to handle the control flow andoutlet member remains pressure biased downwardly Vinto sealed engagementwith surface 138 due t-o the outlet pressure exerted on piston surface124.

During shock conditions, however, the high rates of flow exceed thecapacity of orifice 254 .and develop large forces across shock detectorplate 252 in a direction that lifts outlet member 110-A away fromsurface 138 on the cylinder barrel. When outlet member 11G-A separatesfrom the cylinder barrel, the high volumetric shock flow passes betweenmember 110-A and surface 138 and into the low pressure zone of thehousing. When the shock condition subsides spring 126 and the unbalancedhydraulic force on outlet member 11o-A return it immediately into sealedengagement with surface 138 on the cylinder barrel.

In operation, when the pump is driven by a prime mover cam 44reciprocates pistons 62 which, on the suction stroke, draw oil into thecylinders 78 via inlet passage 84, chamber 86 formed by housing 20, andintake ports 88.

On the compression stroke pistons 62 deliver oil from cylinders 78 tooutlet port 116 via passages 102 in plugs 98, check valves 96, radialpassages 103, annular grooves 104, manifold 134, passage 112 in hollowoutlet member 110, outlet port 116 connected to the load.

Some of the pressurized oil in manifold 134 is delivered to variabledisplacement control apparatus 135 for shifting cam driving piston yandcylinder 146 in the manner previously described.

A constant pressure at the load is obtained by arranging spool 164 toopen only when a predetermined selected load pressure is exceeded.Control knob 172 is adjusted to compress spool control spring 166 so asto bias spool 164 with the proper force to permit its opening when thepredetermined selected operating pressure is exceeded. When the pressureat the load rises above the operating pressure oil from the manifoldpasses through passage 144 and orifice 147 to spool cylinder 148. Theincreased pressure in the spool cylinder overcomes the preset controlforce exerted by spool control spring 166 whereby spool 164 is shiftedto the left, as viewed in FIG. l, and oil is released through radialpassages in spool housing 151 and thence through the previouslydescribed passages to the cam driving cylinder 146. This shifts annularcam driving pist-on 147 and cam mount 161 to the right, as viewed inFIG. l, whereby pumping pistons 62 are moved to the right relative tointake ports 88. This decreases the effective strokes of the pistonssince the intake ports 88 are closed later in the return stroke of thepiston whereby a smaller charge of oil is translated, With less oilbeing pumped per piston compression stroke the pressure is automaticallycut back and when the pressure drops to the preselected control pressurethe biasing force exerted by spool control spring 166 shifts spool 164to the right, as viewed in FIG. l,

f whereby the spool closes radial ports 130 and the flow and passage226, previously described, reaction piston and cylinder means 153 yandspring 151 shift the cam mount 161 and cam 44'towards the left, asviewed in FIG. 1, and thereby shift the pumping pistons to the left toprovide a longer effective stroke for each piston. When this occurs,more oil is delivered to the load per piston stroke. It will, therefore,be understood that the reaction piston and cylinder means 153 and spring151 constantly biases the pump apparatus towards a higher pressureproducing configuration. As soon as the predetermined desired loadpressure is exceeded, however, the previously described pressureproducing action of spool 164 occurs.

In view of the above, it will be understood that the pump operates withspool 164 in a threshold configuration relative to radial passages 130.The moment the manifold pressure exceeds the predetermined pressuredesired at the load, spool 164 departs from its threshold piston andopens to release oil to cam driving cylinder 149. Conversely, the momentthe manifold pressure drops below the predetermined value desired at theload spool 164 maintains radial passages 130 closed whereby oil candrain from cam driving cylinder 149 and permits the cam mount to -drivethe pistons to the left, as viewed in FIG. 1. This increases thevolumetric delivery of oil per piston stroke whereby the pressure at theload is returned to the predetermined value.

While the form of embodiment of the present invention as hereindisclosed constitutes a preferred form, it is to be understood thatother forms might be adopted, all coming within the scope of the claimswhich follow.

I claim:

1. In a hydraulic machine the combination of housing means including aplurality of axially disposed pumping cylinders having side wallsprovided with intake ports and a reaction cylinder communicating with asource of pressurized fluid; piston driving means including a camaxially moveably mounted in said housing means; a plurality of pumpingpistons disposed in said pumping cylinders and in driven engagement withsaid cam; a cam return spring operative between said cam and saidhousing means in one axial direction; an annular reaction piston in saidreaction cylinder for moving said cam in said one axial direction inopposition to reaction forces exerted by said pumping pistons on saidcam, yoke means engaging said pumping pistons; and a pumping pistonreturn spring operative between said yoke and sai-d housing means in theother axial direction.

2. In a hydraulic machine the combination of housing means including aplurality of axially disposed pumping cylinders having side wallsprovided with intake ports and a reaction cylinder communicating with asource of pressurized uid; piston driving means including a cam axiallymovealbly mounted in said housing means; a plurality of pumping pistonsdisposed in said cylinders and in driven engagement with said cam; anannular reaction piston in said reaction cylinder in force transmittingrelationship with said cam in one axial direction; and an annular camdriving piston and cylinder in said housing means in force transmittingrelationship with said cam in the other axial direction, the pressurizedarea of said annular reaction piston being greater than the combinedareas of said pumping pistons.

3. In a hydraulic machine the combination of housing tmeans including acam driving cylinder; a cylinder barrel removeably mounted in saidhousing means and including a plurality of axially disposed pumpingcylinders having side walls provided with intake ports; piston drivingmeans including a cam axially moveably mounted in said housing means; aplurality of pumping pistons disposed in said cylinders and in drivenengagement with said cam; cam return means constantly urging said cammeans in one axial direction; an annular cam driving piston mounted forreciprocating movement in said cam driving cylinder in surroundingrelationship with said cylinder barrel for shifting said cam in ftheother axial direction in' opposition to the force exerted by said camreturn means; and piston return means conlstantly urging said pistonsinto engagement with said cam.

4. In a hydraulic machine the combination of housing means including aplurality of axially pumping cylinders having side walls provided withintake ports; piston driving means including a cam axially moveablymounted in said housing means; a plurality of pumping pistons disposedin said cylinders and in driven engagement with said cam; cam returnmeans including a piston and cylinder communicating with a source ofpressurized fluid for constantly urging said cam means in one axialdirection in opposition to reaction forces exerted by said pumpingpistons on said cam; cam driving means including a piston and cylindercommunicating with a source of pressurized uid for shifting said cam inthe other axial direction in opposition to the force exerted by said camreturn means; yoke means including peripheral portions engaging footportions of said pistons and a central spherical socket portion; a yokedriving member axially shiftably mounted in said housing means andincluding a `second spherical socket portion; a ball in said two socketportions; and a compression spring between said yoke driving member andsaid housing means.

5. In a hydraulic machine the combination of housing means; a removablecylinder barrel mounted in said housing means and including a pluralityof axially disposed pumping cylinders having iside walls provided withintake ports and outlet ports, an annular manifold connecting saidoutlet ports, and a manifold outlet passage including a manifold outletport in an outer wall surface of said barrel; an annular shock reliefmember radially shiftably mounted in said housing means and including aradially disposed iow outlet passage and an inner end engaging saidouter wall surface of said cylinder barrel in surrounding relationshipwith said manifold outlet port; a compression spring between said shockrelief member and said housing means for releasably urging isaid innerend against said outer wall surface; piston driving means including acam axially moveably mounted in said housing means; a plurality ofpumping pistons disposed in said cylinders and in driven engagement withsaid cam; cam return means constantly urging said cam means in one axialdirection; cam driving means for shifting said cam in the other axialdirection in opposition to the force exerted by said cam return means;and pumping piston return means constantly urging said pistons intoengagement with said cam.

6. In a hydraulic machine the combination of housing means; a cylinderbarrel mounted in said housing means and including a plurality ofaxially disposed pumping cylinders having side walls provided withintake ports; a plurality of reaction pins disposed in said pumpingcylinders and including free ends engaging an end of said housing means;piston driving means including a cam axially moveably mounted in saidhousing means; a plurality of pumping pistons disposed in said cylindersand in driven engagementV with said cam; cam return means including areaction piston and cylinder in force transmitting relationship withsaid cam for shifting said cam in one axial direction; cam driving meansfor shifting said cam in the other axial direction in opposition to theforce exerted by said cam return means; and pumping piston return meansconstantly urging said pumping pistons into engagement with saidV cam.

7. In a hydraulic machine the combination of housing mean-s including anaxially disposed pumping piston and cylinder and a piston force reactioncylinder communicating with a source of pressurized uid; and a cam mountaxially shiftably mounted in said housing means and including a reactionpiston portion disposed in said reaction cylinder for biasing said cammount towards said pumping piston in opposition to reaction forcesexerted by said pumping piston.

8. In a hydraulic machine the combination of housing Q l@ Vmeansincluding a cam driving cylinder and a piston 2,578,561 12/51 Lagardelle103--173 X force reaction cylinder, said cylinders communicating2,672,095 3/.54 Lucien etal. 103-173 with pressurized uid source means;a rotatalble cam 2,672,819 3/54 Widmer 103--173 axially shiftablymounted in said housing means be- 2,684,630 7/54 Widmer etal. 103-173tween said two cylinders; a reaction piston in said re- 5 2,732,805 1/56Lucien 103--173 `action cylinder; and a driving piston in said driving2,733,666 2/56 Poulos 10.3-162 cylinder, said driving piston having agreater pressurized 2,945,444 7/ 60 Leissner 103173 X area than saidreaction piston. 2,990,781 7/61 Tuck etal 103-173 X 3,087,432 4/63Budzich 103-173 References Cited by the Examiner 10 F UNITED STATESPATENTS 556 384 7/29ORCEIGN PATENTS 1,710,567 4/29 Carey 10s-162 9107212/58 Nlfyrds 1,817,063 8/31 Carrie et a1. 10s-lf2 2,169,456 8/39Wahlmark 15 LAURENCE V. EFNER, Primary Examzner. 2,369,134 2/45 Cameron103-173 JOSEPH H. BRANSON, JR., Examiner.

1. IN A HYDRAULIC MACHINE THE COMBINATION OF HOUSING MEANS INCLUDING APLURALITY OF AXIALLY DISPOSED PUMPING CYLINDERS HAVING SIDE WALLSPROVIDED WITH INTAKE PORTS AND A REACTION CLYINDER COMMUNICATING WITH ASOURCE OF PRESSURIZED FLUID; PISTON DRIVING MEANS INCLUDING A CAMAXIALLY MOVEABLY MOUNTED IN SAID HOUSING MEANS; A PLURALITY OF PUMPINGPISTONS DISPOSED IN SAID PUMPING CYLINDERS AND IN DRIVEN ENGAGEMENT WITHSAID CAM; A CAM RETURN SPRING OPERATIVE BETWEEN SAID CAM AND SAIDHOUSING MEANS IN ONE AXIAL DIRECTION; AN ANNULAR REACTION PISTON IN SAIDREACTION CYLINDER FOR MOVING SAID CAM IN SAID ONE AXIAL DIRECTION INOPPOSITION TO REACTION FORCES EXERTED BY SAID PUMPING PISTONS ON SAIDCAM, YOKE MEANS ENGAGING SAID PUMPING PISTONS; AND A